1. Field of the Invention
The present invention relates to thermoplastic resin composition with excellent properties such as gas-barrier property, impact resistance, pinhole resistance, stretchability, drawability, and transparency, and also relates to the use of the composition.
2. Description of the Prior Art
Ethylene-vinyl alcohol copolymers with a high vinyl alcohol content are widely used as packaging material for food owing to their superior transparency, gas-barrier property, etc. The Above-mentioned copolymers, however, are rarely used as a mono-layer film since they have insufficient flexibility, processability, stretchability, etc. For example, when these copolymers are molded into film by an inflation process, they have such drawbacks that acceptable molding conditions to obtain satisfactory products from these copolymers are restricted in a narrow range and that longitudinal wrinkles are liable to be formed around pinch rolls. There is another drawback that pinholes are apt to be formed when a film is exposed to repeated deformation such as folding. Such drawbacks can be overcome by blending ethylene polymers, etc., which have excellent flexibility and processability with said copolymer. In many cases, however, addition of ethylene polymers, etc., loses transparency of ethylene-vinyl alcohol copolymers and has not yet been adopted widely.
For example, JP A 40-107351 (1974) discloses that addition of ionomer to ethylene-vinyl alcohol copolymer can improve flexibility. Since this proposal aims at improving adhesiveness of said copolymer to polyolefins, it teaches a technique to add substantial quantities of polyamide as well. This proposal neither considers transparency nor refers to composition of the ionomers.
JP A 50-103582 (1975) discloses an invention which also pays attention to adhesiveness to polyolefins. It discloses laminate containers comprising polyolefins and a composition similar to that in the previous proposal except that the quantity of polyamide blended is smaller. It neither makes consideration on transparency nor discloses use of ionomers in detail although it mentions that zinc ionomer and sodium ionomer can be employed. It only shows examples of using Surlyn 1652 specifically.
According to the investigation of the present inventors, it is revealed that blending of ionomer with ethylene-vinyl alcohol copolymer improves flexibility and processability but deteriorates transparency significantly, and that flexibility and processability are improved but transparency is significantly damaged also in a system in which Surlyn 1652 and polyamide is combined with ethylene-vinyl alcohol copolymer as shown in examples of JP A 50-103582 (1975).
The present inventors then have striven for investigation on composition which overcomes the above-mentioned drawbacks of ethylene-vinyl alcohol copolymer and does not damage transparency so much. As a result, it is revealed that when ionomer of an ethylene-unsaturated carboxylic acid copolymer having high content of unsaturated carboxylic acid component and polyamide are blended at a predetermined ratio, flexibility, processability, impact resistance, tear strength, pinhole resistance, etc., can be improved without sacrificing transparency so much.